The prior art of boat trailers includes a number of simple designs which provide for mobility but do not provide a mechanism for loading and unloading boats or catamarans. Examples of this design include a simple catamaran dolly as disclosed in U.S. Pat. No. 4,243,239 to Whitney. U.S. Pat. No. 4,235,450 to Conover discloses a catamaran dolly having a cradle shaped to engage the hull. A boat trailer having load-bearing arms on a wheeled axle is disclosed in U.S. Pat. No. 3,977,690 to Carn. A simple boat dolly with means for receiving the boat hulls is disclosed in Australian Patent Au-A-14990/83 to Coombe. French Patent No 2,639,893 to Lopez discloses a simple wheeled boat trailer frame. German Patent DE 3147464 A1 to Glodowski discloses a boat trailer with cradles for supporting the hull.
A catamaran-camper trailer having the catamaran straddling the camper vehicle is disclosed in U.S. Pat. No. 4,754,998 to LeJuerrne. An expansible boat trailer is disclosed in U.S. Pat. No. 4,243,242 to Waits, in which a collapsible boat construction is supported by an expanding cradle structure which moves with the hulls to allow boat assembly after transport.
The prior art also includes boat trailers which feature loading and unloading mechanisms, such as in U.S. Pat. No. 4,286,800 to Lomas, which discloses a boat trailer having a load support frame which can be raised and lowered between traveling and unloading positions. The movable load support frame rests on another frame which is supported by wheels upon an axle. Thus, the lowest position of the load support frame is still above the wheeled frame, and this position does not allow unloading of those modern catamaran designs having an especially low profile.
In addition, the Lomas patent describes the raising and lowering mechanism of the load support frame, in which the frame itself is used to transfer the lifting force. When in the lowered position, the load support frame is directly over the wheeled frame and does not act as a lever for lifting, so that set of springs is provided under the load support frame to assist in developing the lifting force. This makes the design complicated, heavy and more costly.
Another difficulty with the use of the trailer disclosed in the Lomas patent is that the construction of the load support frame interferes with the cross-beam between the hulls of modern catamaran designs. This prevents forward or backward adjustment of the catamaran position to balance its weight on the trailer.
In PCT Patent WO 90/01432 to Benest, there is disclosed a trailer for catamarans which can also function as a launch trolley. The trailer comprises a frame having first and second lifting members to apply lifting thrust at spaced locations under the cross-beams of the catamaran. A lever mechanism provides the lifting thrust. In order to unload the catamaran, the trailer is detached from the towing vehicle and partially slid into the water, before operating the lever mechanism to release the lifting thrust. The design is complicated, heavy and expensive.
As with the Lomas patent, the cross-beams between the hulls of the catamaran interfere with the trailer frame to prevent forward or backward adjustment of the catamaran to balance its weight on the trailer. Also, neither the Lomas nor Benest designs allow for loading or unloading of the catamaran assembled with the mast, because the cables supporting the mast interfere with the lifting mechanism, and this interference is also a problem with catamarans having a third crossbeam in front.
With the increase in popularity of modern catamaran designs, the need for an easy-to-use boat trailer has increased. It would therefore be desirable to provide the boating enthusiast with a catamaran trailer which enables him to self-load and unload the catamaran quickly and with minimum inconvenience.